Because atmospheres containing submicron-sized particles, ozone and nitrogen dioxide are considered potentially hazardous to health, studies are proposed which will assess the impact of atmospheres containing these pollutants on murine and lapine pulmonary defense systems. These studies are an extension of ones already performed which indicated that the present air quality standards for sulfate particles and sulfur dioxide or nitrogen dioxide provided at least a three to five fold margin of safety in this test system. In the proposed experiments rodents and one or two day old rabbits will be exposed to high ambient, and above ambient concentrations of submicron-sized sulfate particles, nitrogen dioxide and ozone to determine if these pollutants act additively in inhibiting mucociliary transport 32P-labelled (Staphylococcus aureus), phagocytic ingestion (histologic localization of bacteria), killing of bacteria (measurements of bacterial viability) of intracellular lysosomal enzyme function (histochemical identification of acid phosphatase, beta glucuronidase, lysozyme). These data will be of practical value on deciding a) which kinds of epidemiological measurements are likely to be worthwhile, and b) if it is necessary to revise our present practice of setting standards for each individual pollutant rather than standards for combinations of oxidant and particulate pollutants.